Magnetic latch



A. J. HORNFECQK Oar-" 22; 1940.

. MAGNETIQ LATCH Filed Nov. 2, 193a Inventor-z Anthony J Hornfeck I b flan/ 6 19 9 His ttcr-neg Patented Oct. 22, 1940 UNITED STATES PATENT OFFICE MAGNETIC LATCH Anthony J. Hornfeck, Cleveland, Ohio, assigner F to General Electric Company, a corporation of New York Application November 2, 1938, Serial No. 238,416

2 Claims.

Further objects and advantages of my invention will become apparent as the following description proceeds, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification. I

For a better understanding of my invention reference is had to the accompanying drawing in which Fig. 1 is a view in perspective of the arrangement of the parts of my latch applied to a door; Fig. 2 is a side view, partly in section,

of the details of my latch showing the bolt in the unlatched position; and Fig. 3 is a view similar to Fig. 2 showing the'bolt in the latched position.

In Fig. 1, I have shown a door or closure member ll! adapted to close an opening defined by a door jamb or closure frame member II. In

this embodiment of my invention I have .shown a magnet l2 in a recess 13 in the door jamb H.

A latch bolt l4 spring-biased to the unlatched position is shown carried within a recess [5 in the door Ill. The above-mentioned parts are so ar-' ranged that when the door is closed the magnet I2, whichmust be of sufficient strength to overcome the tension of spring l6, draws the bolt I l into the recess in the door jamb for latching the door.

In order to support the magnet l2 inthe recess 5 I3 I have provided a casing l1 suitably secured in the recess 13 as by means of screws l8. The cas' ing I! should be of non-magnetic material such as-brass, for example, to prevent short circuiting of the magnet I2. The magnet I2 is secured to 40 the casing II by means of a plate IQ of nonmagnetic material such as brass and a-bolt 20 which passes through the plate I9 and magnet I2 and threadingly engages a boss 2| formed in casing I1. I have also provided pole pieces 22 5 having tapered extensions 23 providing. a bolt receiving recess 23a and also having oflset portions or tips 24. These pole pieces andtlpsare of a material of relatively high permeability such as soft steel and may be joined to the magnet l2 in 0 any suitable manner as by soldering or brazing. If desired, the magnet and pole structure may be more securely fastened in casing II by means by an electro-magnet. However, I prefer to use a permanent magnet of high coercive force 'material, such as one containing iron, nickel and aluminum as basic ingredients such as disclosed and claimed in Mishima Patents No. 2,027,994 5 and No. 2,028,000 and Ruder Patents Nos.- 1,947,- 274; and 1,968,569, although the magnet may contain other ingredients such as cobalt, tungsten, molybdenum, silicon, copper and titanium, for example. Because of the fact that soft'steel has 10 a higher permeability than the magnet material described there will be a greater flux density in the pole pieces 22 and tips 24 than if the pole pieces and tips were of the same material as the magnet, thereby providing a greater holding 15 force.

tained in recess I5 in any desired fashion as by means of screws 21. Latch bolt I4 is slid-' ably retained in the upper portion of casing 26 20 and is biased toward the unlatched position, or, the right as viewed in the drawing, by means of spring I6 interposed between shoulder 28 which extends from the casing 26 into a slot 29 formed in the bolt l4 and the right-hand end of the slot 257 29. With this arrangement the spring I6 is under compression in the latched position but it will be obvious that, if desired, a tension spring might be substituted-between the inner end of the latch bolt I4 'and the end of casing 26. 3o

The tapered bolt design enables a small magnet to be used for exerting a lateral pull on the bolt it over a relativelylarge distance. If no pole I pieces were employed a much more powerful magnet would be required to exert any appreciable pull on the latch bolt when the bolt is in the position shown in Fig. 2 as will be clear from the following considerations.

In order to latch the door a recess-must be provided to receive thebolt and since .the magnet 40 is placed at the inner end of the recess it is ob- .vious that a comparatively large air gap exists between the magnetandthe bolt when the boltis v in the unlatched position. By extending the 'pole' pieces to the front edge of the recess IS, the

air gap is reduced to the distance between the endsyof the pole pieces and the latch bolt,- in other iwords, substantially to the space between the door l0 andthe door jamb II. If the pole pieces 22 are not tapered, the latch bolt M willbe drawn to a position opposite the ends of the pole pieces 22 but, practically speakinggthere will-be no active force'tending to pull the bolt m the fully latched position. By providing the pole pieces '22 with a-taper, the air gap between the pole pieces 22 and latch bolt ll gradually decreases until the bolt It strikes the onset tips;

24."- Thus, there is always a constantly 1110 1 ing force acting to seat the bolt during the latch-- ing operation. It mayalsobenotedthatthetapered constructionassists in centering the bolt,

thereby counteracting any sagging of the door. The offset tips 24 are provided adjacent the bottom of recess 23a in order to concentrate the flux and thereby increase the holding force in the latched position.

In order to retract the bolt for opening the door, I have provideddoor knobs 3| secured in the customary fashion to a shaft 32 -extending through the door ill and also through the slot 29 in the bolt l4. A pinion 33 is carried by shaft 32 and has teeth 34 for engagement with a rack 35 cut in the inner edge of the slot 29. It will be obvious from an inspection of the drawing that as the door knob is turned in a clockwise direction as viewed in Fig. 3, the teeth 34 willmesh with the rack 35 and impress a force on latch ll to withdraw the latch from the influence of magnet l2. opening the door is purely illustrative and any desired arrangement may be used.

I have also provided means to lock the latch in the closed position. For this purpose I have provided a catch 31 adapted to project into a recess 33 formed in the underside of bolt l4. As shown in the drawing, the catch 3'1 is guided by means of pins 310 attached to casing 26 which extend into a slot 31b formed in the catch 31. The catch 31 is held in the unlocked position by means of a spring arm 39 which has a portion 30 pressing into a recess 3| in the catch 31. The door may be locked by inserting a key 42 into keyhole 43. By turning the key in a clockwise direction as viewed in Fig. 2, the key will engage projections 44 on catch 31. The upward force transmitted to latch 31 will cause portion 40 of arm 39 to be forced out of the recess 4| and raise the catch 31 upwardly into engagement with recess 38 at which position the portion. of spring arm-33 will presss into recess 45 in latch 31, thereby to hold the catch 31 in the looking position. In order to unlatch the door, the key must be turned in a counter-clockwise direction as viewed in Fig. 3 in order to engage teeth 14 and press the latch 31 downwardly as will be obvious by inspection of Fig. 3. The above description of this locking mechanism is also exemplary and any desired locking arrangement may be employed. For example, the catch may be pressed into locking engagement with bolt Hi from any direction and, if desired, instead of the spring arm 39, a spring-biased catch couldbe used so that the door would be locked automatically upon closing.

Spring l8 may be eliminated, if desired, and a second magnet of lesser strength than magnet I! may be employed to hold latch, 14 in the open position. When the door is closed, the excess of strength of magnet I! will draw the bolt M into the latched position. If desired, instead of substituting a second magnet for spring IS, a second magnet may be added to supplement the action of spring I 6.

It will also be obvious that the latch bolt may be carried by the door lamb and the magnet secured to the door.

While I have shown a particular embodiment of my invention in connection with a magnetic door latch, I do not desire my invention to be limited to the particular construction shown and described. For instance, my invention is equally applicable wherever a\movable member is to be drawn to and held by asecond member, assuming that it is possible to use magnetic materials,

The above-described means for 4 Letters Patent of the United States is:

1. In a magnetic latch, the combination of a closure member, a closure frame member, a permanent magnet formed of high coercive force material disposed in a recess in one of said members, a latch bolt of magnetic material slidably arranged in a recess in the'other of said members, said magnet being provided with a plurality of pole pieces formed from a material of higher permeability than said magnet in order to obtain a relatively high flux density in said pole pieces, said pole pieces extending beyond said magnet and providing a recess for the reception of said bolt, the ends of said pole pieces being substantially flush with the edge of said one of said members and the outer edge of saidbolt being substantially flush with the edge of said other of said members in the unlatched position of said bolt in order to provide a relatively small air gap between said pole pieces and said bolt in the unlatched position of said bolt, said bolt being so manent magnet formed of high coercive force material disposed in a recess in one of said members, a latch bolt of magnetic material slidably arrangedin a recess in the other of said members, said magnet being provided with a plurality of pole pieces formed from a material of higher permeability than said magnet in order to obtain a relatively high flux density in said pole pieces, said polepieces extending beyond said magnet and providing a recess for the reception of said bolt, the ends of said pole pieces being substantially flush with the edge of said one of said members and the outer edge of said bolt being substantially flush with the edge of said other of said members in the unlatched position of said bolt in order to provide a relatively small air gap between said pole pieces and said bolt in the unlatched position of said bolt, said bolt being so positioned on said other of said members that said bolt willbe drawn by said magnet into the bolt receiving recess when said closure member is in its closed position, said pole pieces and said bolt being provided with tapering portions .50 that when said bolt is drawn toward said magnet, the airgap between said pole pieces and said bolt will constantly decrease whereby there is a constantly increasing force acting to seat said bolt during the latching operation, each of said pole pieces having an offset portion adjacent the bottom of said bolt receiving recess for receiving said bolt and concentrating the flux in the latched position of said bolt, thereby increasing the holding force of said magnet onsaid bolt.

ANTHONY J. HORNFECK. 

